The present invention relates generally to orthodontic devices and more particularly to an assembly for orthodontic brackets applied to teeth which are to be orthodontically treated. The type of bracket involved with the invention includes a base which is secured to a respective tooth and bracket wings which extend laterally on both sides of the brackets and which define therebetween a central slot adapted to receive therein a regulating arch. The invention also relates to a method for preparation in the laboratory of the bracket assembly and for application of the bracket to a tooth.
Brackets of the type to which the present invention relates have been heretofore temporarily secured upon a positive jaw model in proper position for regulation. An elastic mold negative or transfer matrix is then produced to receive the brackets and by means of this matrix the brackets are transferred to teeth in the mouth and are cemented thereupon.
The materials for forming the transfer matrix have generally been composed of soft rubber materials having a modulus of elasticity of between about 700 to 1000 kg/cm.sup.2 and a wall thickness of between about 2 to 4 mm. These characteristics are related mainly to providing the transfer matrix with an ability to be detached from the orthodontic device after the bracket is cemented in the mouth inasmuch as the matrix material will usually extend beneath the bracket wings and it can be easily detached with provision of an appropriate or corresponding elasticity of the matrix material. Such soft elastic matrix material usually requires a considerable wall thickness in order to obtain a sufficient stability of form. Furthermore, the transfer matrix must extend sufficiently far over the teeth and into the range of the gums. This is generally an unfavorable characteristic inasmuch as the gums are subject to constant change and there may thus be caused incorrectness in the application of the bracket when the matrix is later applied in the mouth. Additionally, when the transfer matrices are applied upon the teeth, squeezing of the adhesive in the mouth is unavoidable. In a particularly unfavorable situation, adhesive may even flow into the interdental spaces thereby leading to blockage between the teeth and making the regulating forces of the orthodontic apparatus ineffective. Furthermore, uncontrollable excess adhesive may be formed under the projecting transfer matrices on the teeth outside of the bracket base thereby causing difficulty and time-consuming procedures when removal is necessary after hardening.
Furthermore, metal brackets with perforated bases have the disadvantage that the material of the transfer matrix tends to penetrate into these perforations. The transfer matrix can consequently not be readily molded over such a bracket. It has, therefore, been suggested to secure the metal brackets with adhesive upon the model teeth before the transfer matrix is formed so that adhesive can penetrate into the perforations of the metal base and fill them. When the prepared bracket is later cemented upon teeth in the mouth, another coat of adhesive establishes at that point a bond with the teeth. However, insulation problems arise on the model teeth. The model teeth may be so well shielded by conventional insulating means that the adhesive will not adhere to the material of the model. However, the bracket does not then have the necessary holding characteristics for the production of the transfer matrix. Also, the brackets may adhere firmly on the model tooth because the insulation is less effective but in such a case layers or particles of the model material will stick to the bracket base when the matrix is lifted and they must be removed with great effort.
It has, accordingly, been attempted to affix brackets with a temporary adhesive on model teeth. It is known to use as a temporary adhesive pasty mixtures of corn flour, potato starch and water. In such cases, the temporary adhesive must be later removed completely from the brackets received in the transfer matrix. This is difficult because remnants of the temporary adhesive tend to become stuck between the matrix and the bracket base.
Additionally, in none of the known methods is it possible to take into consideration a further important condition, namely, the fact that the adhesive not only fills the perforations of the bracket bases but also covers or surrounds them in the range of the perforations and at the edges of the bases with a thin uniform layer. This also applies to plastic brackets without perforations in the bracket base. This occurs in order to insure the riveting effect necessary to hold the brackets on the teeth in the mouth. With the small dimensions of the brackets and their bases, it is practically impossible to apply the riveting adhesive layer by hand with the necessary dimension either on the model or in direct cementing of the brackets upon the teeth in the mouth.
Accordingly, it is an object of the present invention to provide a solution to the aforementioned problems whereby brackets of the type in question may be first temporarily secured upon model teeth in a simple and clean manner and may be subsequently transferred by means of the transfer matrix to the teeth in the mouth and cemented thereon.